This disclosure relates to couplers, more particularly but not necessarily exclusively, for coupling support structures for supporting a trampoline sheet.
A typical trampoline comprises a sheet, usually, though not invariably, circular, supported around its periphery within a frame like support structure by spring couplings (usually a plurality of helical springs or an elastic cord) under tension which link apertures around the edge of the sheet to, openings in the frame. The frame will generally have a configuration that matches that of the trampoline sheet. Thus, when the trampoline sheet is circular, the frame will usually take the form of a generally circular ring with a diameter larger than that of the sheet in order that the sheet is stretched. When the trampoline sheet is rectangular in shape, the frame will usually comprise a ring of generally rectangular form that is similarly larger than the sheet in order that the sheet may be supported by helical springs under tension. The frame must be supported above the ground or floor. A typical trampoline support structure comprises a plurality of tubular members adapted to fit together to form the particular configuration of frame. At least some of the tubular members have a stub pipe welded thereto, which is adapted to interfit with an upper end of a respective leg, the several legs together supporting the frame and the trampoline sheet above the ground or floor. The respective legs are suitably tubular and pairs of legs will typically be formed from a single tube bent into a generally U- or W-shape in which the uprights of the U or W form the legs proper, the lower ends of which are interconnected by the bight portion of the U or the central portion of the W. In the case of a U-shaped structure, the bight portion of the U provides support from the floor or ground, whereas in a W-shaped structure the lower angular corners of the “W” serve the same purpose.
Trampolines in normal use are subjected to repeated stress. When used contrary to the manufacturer's instructions, for example on an uneven surface, by being dragged from one position to another, by a user jumping from an off-centre position, and when more than one person is on the trampoline at any one time, they are stressed unevenly, and often excessively. Moreover, they are often treated as garden equipment and left out in the cold and wet. As a result, corrosion or splitting of the welds between the tubular members and the stub pipes may occur over time, weakening the structure, potentially giving rise to a dangerous accident for a trampoline user.
In one attempt to overcome this problem, Thomas A James proposes a structural coupler for joining the tubular members and the legs in US 2004/0091307. The coupler is substantially T-shaped, providing a cross member support tube for receiving ends of tubular members of the frame and an intersecting support tube for receiving the upper end of a leg. The coupler avoids welds by starting from a single piece of pre-formed metal bending it to create a complete tube and a complete cross member. Seams are formed at overlapping edges, the seams running up sides of the intersecting tube member and then along the undersides of the cross-member. Either the seaming must be performed on site about butted or overlapping ends of two tubular members and about the upper end of a leg to form the coupler in situ, or the coupler is preformed and seamed off site and ends of tubular members and the upper end of a leg are force fitted on site into the ends of the cross member and into the intersecting support tube. The first arrangement requires skilled operatives and so is impractical, the second does not provide a sufficiently reliable join.
In an alternative arrangement, Arthur Chu in AU2006100018 suggests avoiding welds by employing a coupler comprising a sleeve into which respective ends of tubular members forming the frame are loosely received with the end of one such tubular member located within the other. The sleeve is incomplete, its bottom wall being split, each half thereof being integral with one half of a split tubular portion, the two halves of which are adapted to be forced into the female opening at the upper end of a leg. The interfitted ends of the frame tubular members have through apertures. These are aligned with inwardly directed studs on the sides of the sleeve so that, as the split tubular portions are forced into the upper end of a leg, the sides of the sleeve are drawn together and the inwardly directed studs interengage with the aligned apertures. In this arrangement satisfactory holding of the frame tubular members is dependent upon the apertures and studs being aligned and upon the extent by which the split tubular portions are received within the leg. In practice reliable location of the split tubular portions in the upper end of the leg is difficult to achieve, and the connection is insufficiently reliable in use.